The present invention relates generally to methods and apparatus for heating and cooling patients for therapeutic purposes, and more particularly to systems for treating brain trauma and brain ischemia by inducing hypothermia in a patient.
It has been discovered that the medical outcome for a patient suffering from severe brain trauma or from ischemia caused by stroke or heart attack is degraded if the patient""s body temperature rises above normal (38xc2x0 C.). It is further believed that the medical outcome for many such patients might be significantly improved if the patients were to be cooled relatively quickly to around 32xc2x0 C. for a short period, e.g., 24-72 hours.
The affected organ, in any case, is the brain. Accordingly, systems and methods have been disclosed that propose cooling blood flowing to the brain through the carotid artery. An example of such systems and methods is disclosed in co-pending U.S. patent application Ser. No. 09/063,984, filed Apr. 21, 1998, owned by the present assignee and incorporated herein by reference. In the referenced application, various catheters are disclosed which can be advanced into a patient""s carotid artery and through which coolant can be pumped in a closed circuit, to remove heat from the blood in the carotid artery and thereby cool the brain. The referenced devices have the advantage over other methods of cooling (e.g., wrapping patients in cold blankets) of being controllable, relatively easy to use, and of being capable of rapidly cooling and maintaining blood temperature at a desired set point.
As recognized in co-pending U.S. patent application Ser. No. 09/133,813, filed Aug. 13, 1998, owned by the present assignee and incorporated herein by reference, the above-mentioned advantages in treating brain trauma/ischemic patients by cooling can also be realized by cooling the patient""s entire body, i.e., by inducing systemic hypothermia. The advantage of systemic hypothermia is that, as recognized by the present assignee, to induce systemic hypothermia a cooling catheter or other cooling device need not be advanced into the blood supply of the brain, but rather can be easily and quickly placed into the relatively large vena cava of the central venous system. Moreover, since many patients already are intubated with central venous catheters for other clinically approved purposes anyway, providing a central venous catheter that can also cool the blood requires no additional surgical procedures for those patients.
Regardless of where the cooling occurs, however, it is clear that heat must be removed from the coolant that flows through the catheter. As recognized herein, it is desirable that a cooling system for a cooling catheter consume minimal energy and space. Small size is desired because space is often at a premium in critical care units. Moreover, as also recognized herein, for patient comfort it is desirable that such a cooling system generate a minimum amount of noise. As still further understood by the present invention, it is desirable that the cooling system be easy to use by health care personnel, and that the portion of the cooling system that directly contacts the catheter coolant be disposable. We understand that if the portion of the cooling system that directly contacts the catheter coolant were not disposable, the portion undesirably would require sterilization by, e.g., autoclaving prior to reuse, because even though the coolant does not directly contact the patient but is instead contained within the catheter, the potential arises that through in-leakage or other means body fluid might indeed contaminate the coolant. Accordingly, it is the object of the present invention to address one or more of the above-noted considerations.
A heat exchange system for a catheter includes at least one heat exchange element that is connectable to the catheter for receiving coolant from the catheter, and at least one thermal electric cooler (TEC) in thermal contact with the heat exchange element for heating or cooling the element such that coolant is returned to catheter to heat or cool the catheter.
In a preferred embodiment, the heat exchange element is plastic. More preferably, the heat exchange element includes plural hollow fibers, or, the heat exchange element can include at least one non-linear plastic tube. As another alternative, the heat exchange element can include a bag that has plural fluid paths through the bag which are established by, e.g., heat-staking portions of the bag together. A thermal interface such as an aluminum oxide gel or metallized plastic foil bag can be sandwiched between the heat exchange element and the TEC to removably couple the element to the TEC. Less desirably, the heat exchange element includes at least one metal tube in thermal contact with the TEC. For cooling efficiency, two cooling stages can be used, with each cooling stage including a respective heat exchange element with associated TEC assembly, and at least one thermal barrier is disposed between the elements.
In another embodiment, a heat exchange fluid is disposed between the TEC and the heat exchange element such that the heat exchange element is disposed in the fluid. The fluid can be cold ethylene glycol. An agitator is disposed in the fluid to move the fluid.
In another aspect, a cooling system for a therapeutic medical device includes at least one heat exchanger made at least partially of plastic. The heat exchanger receives coolant from the medical device and returns coolant thereto. A thermal electric cooler (TEC) is in thermal contact with the heat exchanger for removing heat from the heat exchanger.
In still another aspect, a cooling system includes catheter means for conveying coolant into a patient""s body without directly contacting the coolant with the body. Also, the system includes heat exchanger means communicating with the catheter means for receiving coolant therefrom and returning coolant thereto. Cooling means is in thermal contact with the heat exchanger means for conveying heat away from the heat exchanger means.
In yet another aspect, a controller is disclosed for establishing a control signal for controlling coolant temperature in a therapeutic catheter cooling system. The cooling system can include a coolant pump and at least one TEC, and the controller includes logic means that receive a desired patient temperature and a measured patient temperature. The controller logic determines a control signal in response to the temperatures, with the control signal being sent to the cooling system for establishing the coolant temperature. Preferably, the control signal is also established in accordance with a measured patient temperature time derivative and/or time integral. As intended by the present invention, the control signal is used to establish at least one of: a speed of the coolant pump, and an energization of the TEC.
The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which: